The present invention relates to a method of measuring the lime content of a powdery product, comprising the steps of introducing a determined quantity of the powdery product and a determined quantity of a solvent into a recipient, agitating this mixture so as to dissolve the lime in the solvent, and measuring in this mixture an electrical characteristic representing said lime content.
The invention also relates to a device for measuring the content of a soluble component in a powdery product, comprising at least one recipient, means for dosing a given quantity of a solvent and bringing it to said recipient, means for dosing a given quantity of the powdery product and bringing it to the recipient, means for agitating the contents of the recipient, means for measuring an electrical characteristic in the contents of the recipient, and means for discharging the contents of the recipient after this measurement.
The invention applies particularly, but not exclusively, to the measurement of the free lime content of cement or cement clinker.
In cement works such a measurement is regularly made on a sample of clinker taken from the kiln exit, then cooled and crushed, with the object of controlling the production, especially the burning process in the kiln.
French Pat. No. 2 163 963 describes a method and a device for carrying out this measurement in a manner allowing automatic operation of a cement plant kiln. One uses in this case a device comprising on one hand a chamber, in which a mixture of the crushed clinker sample and heated glycol is prepared and an electrical characteristic of this mixture is measured, and on the other hand means for supplying dosed volumes of clinker and glycol to this compartment. The dosing and supply means for the crushed clinker are described in more detail in French Pat. No. 2 182 283 and comprise a calibrated assay crucible, into which the clinker is poured and packed, then levelled to constitute the desired volume. This crucible is next brought mechanically by a mobile arm above the chamber to empty the clinker into it.
This operating mode and this device still have various drawbacks which affect the precision of the measurement and the reliability of the process, and hence also the quality of the clinker produced in the kiln in the case of automatic operation. First of all the density of the crushed clinker sample may vary, in particular with the granulometry of the sample. This occurs especially in the case of malfunction of the kiln, producing an "unburnt" clinker whose grindability differs from that of normal clinker. As a result, the quantity of clinker introduced into the measuring chamber also varies and the measurement is given an erroneous value. Now, it is precisely in such a case that the production has to be corrected.
On the other hand, the volumetric determination of the quantities with this device does not allow for control in an automatic process. If one of the supply devices malfunctions, the measurement may be effected on false quantities, for example if the calibrated assay crucible is not completely filled with clinker before levelling. The same applies in the case of malfunction of the pump for glycol.
In addition, the measuring chamber is a complex and delicate instrument. In particular, its complete evacuation between two operating cycles is not always ensured, because the valves may be obstructed. The displacement of the mobile electrode which it contains is also subject to faulty operation.
Consequently, the present invention has the object of meeting these drawbacks, by providing a method of the type mentioned in the preamble and allowing precise and reliable measurement of the lime content to be achieved, by means of a device including relatively simple and proven components. The invention shall particularly ensure highly reliable operation of the successive measurements carried out during automatic operating cycles of the device, in order to be fit for use in an automatic system for controlling the production of the powdery product.